Apparatus and method for calibrating span of pressure measuring instruments

Abstract

A differential-pressure transmitter having a range diaphragm and a slack diaphragm to receive process pressures and to apply such pressures to an interior sealed chamber containing a fill-liquid. An internal passageway between the regions adjacent the diaphragms provides for transfer of fill-liquid in response to differential pressure changes. The passageway serially includes a vertically-oriented tube containing a ball of magnetic material and surrounded by a solenoid winding. Energization of the winding lifts the ball to the top of the tube. When the winding is de-energized, the ball drops down through the fill-liquid to create a reference pressure pulse which is directed to the range diaphragm to correspondingly alter the instrument output signal. The output signal is monitored to check the span calibration, and adjustments are made as needed.

What is claimed is: 
     
       1. In a pressure measuring instrument of the type including a sealed interior pressure chamber containing a fill-liquid and having diaphragm means to apply thereto an input pressure signal to be measured, said instrument further including sensing means responsive to the input pressure signal applied to said fill-liquid to produce a corresponding output signal; that improvement for calibrating the span of the instrument comprising:   reference pressure means forming in integral part of said instrument and including means in communication with said fill-liquid to apply thereto a reference pressure of precisely-controlled predetermined magnitude; and   said reference pressure means being activatable while said input pressure signal is stable to apply said reference pressure to said fill-liquid so as to produce from said sensing means an output signal corresponding to said reference pressure magnitude;   whereby the span of the instrument can be monitored and adjusted as necessary to assure that the output signal will correspond exactly to said reference pressure magnitude.   
     
     
       2. Apparatus as in claim 1, wherein said reference pressure means comprises means defining a cavity containing fill-liquid in communication with said instrument fill-liquid; means operable with said cavity to develop said reference pressure; and   means to activate said reference pressure means.   
     
     
       3. Apparatus as in claim 2, wherein said instrument comprises a pair of diaphragms to receive a differential input pressure to be applied to said instrument fill-liquid; the fill-liquid regions adjacent said diaphragms being connected by a passageway;   said cavity forming part of said passageway.   
     
     
       4. Apparatus as in claim 2, wherein said reference pressure means further comprises an element in contact with said cavity fill-liquid; and means to effect movement of said element in said cavity to create said reference pressure in said cavity fill-liquid.   
     
     
       5. Apparatus as in claim 4, including electrically-operable means to effect said movement. 
     
     
       6. Apparatus as in claim 4, wherein said cavity is formed to provide an elongate dimension; said element comprising an object sized to move through said elongate dimension to produce said reference pressure.   
     
     
       7. Apparatus as in claim 6, wherein said means to effect movement comprises means to rail said object against the force of gravity and then to release said object to allow it to fall under the force of gravity to produce said reference pressure. 
     
     
       8. Apparatus as in claim 7, wherein said means to effect movement comprises magnetic means operable in response to a signal to raise said object. 
     
     
       9. Apparatus as in claim 8, wherein said magnetic means comprises a coil energizable by said signal. 
     
     
       10. Apparatus as in claim 7, wherein said object is a ball; said cavity comprising a cylindrical tube having a circular cross-section slightly larger than the diameter of said ball.   
     
     
       11. Apparatus as in claim 10, including a winding surrounding said tube for producing a magnetic field for raising said ball. 
     
     
       12. In a pressure measuring instrument of the type including means to receive an input pressure signal and sensing means responsive to said input pressure signal to produce a corresponding output signal; that improvement for calibrating the span of the instrument comprising:   reference pressure means forming an integral part of said instrument and including a cavity containing fill-liquid in communication with said sensing means; and   means to activate said reference pressure means while said input pressure signal is stable to develop in said fill-liquid a reference pressure of precisely-controlled predetermined magnitude so as to apply a corresponding force to said sensing means to develop therefrom an output signal corresponding to said reference pressure magnitude;   whereby the span of the instrument can be monitored and adjusted as necessary to assure that the output signal will correspond exactly to said reference pressure magnitude.   
     
     
       13. Apparatus as in claim 12, wherein said reference pressure means further comprises an element in contact with said cavity fill-liquid; and means to effect movement of said element in said cavity to create said reference pressure in said cavity fill-liquid.   
     
     
       14. Apparatus as in claim 13, including electrically-operable means to effect said movement. 
     
     
       15. Apparatus as in claim 13, wherein said cavity is formed to provide an elongate dimension; said element comprising an object sized to move through said elongate dimension to produce said reference pressure.   
     
     
       16. Apparatus as in claim 15, wherein said means to effect movement comprises means to raise said object against the force of gravity and then to release said object to allow it to fall under the force of gravity to produce said reference pressure. 
     
     
       17. Apparatus as in claim 16, wherein said means to effect movement comprises magnetic means operable in response to a signal to raise said object. 
     
     
       18. Apparatus as in claim 17, wherein said magnetic means comprises a coil energizable by said signal. 
     
     
       19. Apparatus as in claim 16, wherein said object is a ball; said cavity comprising a cylindrical tube having a circular cross-section slightly larger than the diameter of said ball.   
     
     
       20. Apparatus as in claim 19, including a winding surrounding said tube for producing a magnetic field for raising said ball. 
     
     
       21. In a pressure measuring instrument of the type including a sealed interior pressure chamber containing a fill-liquid and having a pair of diaphragms through which an input differential pressure may be applied to said fill-liquid, said instrument further including sensing means responsive to said differential pressure to produce a corresponding output signal; that improvement for calibrating the span of the instrument comprising:   (1) reference pressure means forming an integral part of said instrument and including: (A) means forming a cavity having an elongate dimension;   (B) a fill-liquid in said cavity in communication with said instrument fill-liquid;   (C) an object in said cavity sized to provide a close fit with the cavity walls;   (D) means to lift said object up in said cavity and to release the object for descent through said fill-liquid under the force of gravity to produce in said fill-liquid a highly-precise pressure pulse of substantially constant magnitude; and     (2) means to activate said lifting means while said input differential pressure is zero to apply said reference pressure pulse to said fill-liquid so as to produce from said sensing means an output signal corresponding to said reference pressure magnitude;   whereby the span of the instrument can be monitored and adjusted as necessary to assure that the output signal will correspond exactly to said reference pressure magnitude.   
     
     
       22. Apparatus as in claim 21, wherein one of said diaphragms is a range diaphragm having a pre-set spring-rate and effective area; said reference pressure means being arranged to apply said reference pressure to said range diaphragm.   
     
     
       23. Apparatus as in claim 22, including a conduit leading from the lower end of said cavity to the region adjacent said range diaphragm. 
     
     
       24. Apparatus as in claim 21, wherein said output signal is electrical and said activating means comprises electrical-signal-responsive means; signal-monitoring means coupled to said instrument to receive the output signal thereof; and   signal means adjacent said signal-monitoring means and coupled to said activating means to direct thereto an electrical signal for initiating an operation of said reference pressure means.   
     
     
       25. Apparatus as in claim 24, wherein said signalmonitoring means and said signal means are remote from said instrument. 
     
     
       26. Apparatus as in claim 25, including a valved manifold connecting the differential pressure to said diaphragms; and means for actuating the manifold valves to provide zero differential pressure to said instrument;   said actuating means including means at said remote location for controlling the operation of said manifold.   
     
     
       27. Apparatus as in claim 24, wherein said cavity is formed by a cylindrical tube and said object comprises a ball in said tube. 
     
     
       28. The method of calibrating a pressure measuring instrument of the type having pressure-responsive diaphragm means arranged to receive an input pressure signal and to seal an interior chamber containing a fill-liquid to which the input pressure signal as applied, said instrument further including sensing means responsive to the pressure signal applied to said fill-liquid for developing a corresponding output signal; said method comprising the steps of: operating a device forming part of said instrument to apply a reference pressure signal of predetermined magnitude originating therein to said fill-liquid while the input pressure signal at said diaphragm means is stable;   monitoring said output signal to determine whether it is at the correct magnitude for the applied reference pressure signal; and   making such adjustment as is necessary to conform the instrument output signal to said correct magnitude upon subsequent application of said reference pressure signal.   
     
     
       29. The method of claim 28, wherein said reference pressure signal is developed by causing an object to move in a cavity containing said fill-liquid. 
     
     
       30. The method of claim 29, wherein said object is caused to move through at least a part of said cavity by the force of gravity. 
     
     
       31. The method of claim 30, wherein said object is first raised against the force of gravity by an externally-developed magnetic field, and then allowed to descend through the fill-liquid. 
     
     
       32. The method of claim 28, including the step of maintaining static pressure on said diaphragm means while operating said device. 
     
     
       33. The method of determining the temperature of a pressure measuring instrument of the type having pressure-responsive diaphragm means arranged to receive an input pressure signal and to seal an interior chamber containing a fill-liquid to which the input pressure signal is applied, said instrument further including sensing means responsive to the pressure signal applied to said fill-liquid for developing a corresponding output signal; said method comprising the steps of: developing a reference pressure pulse by causing an object to move in a cavity containing said fill-liquid; and   measuring the duration of said pulse to provide an indication of the temperature of the fill-liquid thereby providing a measure of the temperature of the instrument.   
     
     
       34. The method of claim 33, wherein said object is caused to move through at least a part of said cavity by the force of gravity.